the National Natural Science Foundation of China under Grant No.60573126(国家自然科学基金);the National High-Tech Research and Development Plan of China under Grant Nos.2007AA04Z148, 2007AAO1Z149(国家高技术研究发展计划(863));the National Basic Research Program of China under Grant No.2002CB312005(国家重点基础研究发展计划(973))